Chapter 3. Creating a Virtual Machine

After you have installed the virtualization packages on your Red Hat Enterprise Linux 7 host system, you can create virtual machines and install guest operating systems using the virt-manager interface. Alternatively, you can use the virt-install command-line utility by a list of parameters or with a script. Both methods are covered by this chapter.

3.1. Guest Virtual Machine Deployment Considerations

Various factors should be considered before creating any guest virtual machines. The role of a virtual machine should be evaluated before deployment, but regular monitoring and assessment based on variable factors (load, amount of clients) should also be performed. The factors include:
Performance
Guest virtual machines should be deployed and configured based on their intended tasks. Some guest systems (for instance, guests running a database server) may require special performance considerations. Guests may require more assigned CPUs or memory based on their role and projected system load.
Input/Output requirements and types of Input/Output
Some guest virtual machines may have a particularly high I/O requirement or may require further considerations or projections based on the type of I/O (for instance, typical disk block size access, or the amount of clients).
Storage
Some guest virtual machines may require higher priority access to storage or faster disk types, or may require exclusive access to areas of storage. The amount of storage used by guests should also be regularly monitored and taken into account when deploying and maintaining storage. Make sure to read all the considerations outlined in Red Hat Enterprise Linux 7 Virtualization Security Guide. It is also important to understand that your physical storage may limit your options in your virtual storage.
Networking and network infrastructure
Depending upon your environment, some guest virtual machines could require faster network links than other guests. Bandwidth or latency are often factors when deploying and maintaining guests, especially as requirements or load changes.
Request requirements
SCSI requests can only be issued to guest virtual machines on virtio drives if the virtio drives are backed by whole disks, and the disk device parameter is set to lun in the domain XML file, as shown in the following example: 
<devices>
  <emulator>/usr/libexec/qemu-kvm</emulator>
  <disk type='block' device='lun'>